Adenosine has been proposed to play an important role in the regulation of coronary blood flow (CBF). To date, there have been very few studies which examined the relationship between adenosine and other vasoactive agents (K+, H+, Pi and osmolality in the regulation of CBF and their mechanims of action at a molecular or cellular level. A combination of models (isolated perfused hearts, isolated cardiac, vascular smooth and endothelial cells and intact vascular strips) will be utilized in this project. These studies together with the reported studies in the literature should provide a clearer understanding of the role of adenosine and other vasoactive agents and their relationship in the metabolic regulation of CBF The proposed studies on coronary vascular smooth muscle and endothelial cells will provide information in regard to the contribution of coronary vessels with special emphasis on the role of adenosine and other vasoactive agents. Thus, the main objectives of this proposal are to study: (a) evidence for the existence of an adenosine receptor in coronary vessels utilizing intact vessels and isolated plasma membranes from these vessels; (b) the release of adenosine and vasoactive agents due to increases in beating rate following various manipulations in isolated cardiac cells and their relationship to O2 consumption; (c) the release (due to graded hypoxia), metabolism and pathways involved in the synthesis and degradation of adenosine in vascular smooth muscle and endothelial cells; (d) the metabolism of adenosine under hypoxic conditions and its relationship to coronary flow, high energy phosphate levels, and the regulation of adenosine metabolizing enzymes in intact perfused hearts; (e) the metabolic regulation of CBF in relation to the contribution of each metabolite and their relationships using isolated perfused hearts; and (f) the effects of adenosine on ion fluxes in isolated vascular smooth muscle cells. In summary, the data derived from these studies should represent a major advance in our understanding of local CBF regulation at a molecular and cellular level, and should provide a rational basis for therapeutic alterations of regional blood flow in low flow states such as coronary insufficiency, myocardial infarction and cardiac hypertrophy.